Vpr and Vpx arose by an ancestral recombination event, and confer diverse properties upon primate lentiviruses, including the ability to replicate in quiescent cells. Vpr and Vpx are packaged into virions in amounts comparable to Gag proteins and mediate the transport of preintegration complexes into the nucleus of non-dividing cells. The current proposal is for continuation of studies of the novel packaging determinants of Vpr and Vpx, dissection of the preintegration complex transport mechanisms, and exploration of interactive cellular proteins that may mediate these and other activities. The specific aims address the following question: 1. What are the determinants of Vpr/x Packaging into Virions and how do they work? a. What are the sequence determinants in Vpx for Packaging? b. What are the sequence determinants in HIV-2 Gag for Vpx Packaging? c. What are the sequence determinants for HIV-2 Vpr Packaging? 2. What are the roles of Vpr/x in Preintegration Complex Transport into the Nucleus? a. What is the role of Vpr phosphorylation in nuclear transport? b. What determinants of HIV-1 Vpr regulate preintegration complex transport? c. What determinants of Vpx regulate preintegration transport? 3. What are the roles of Vpr/x Interactive Cellular Proteins in HIV Infection? a. What is the role of li interaction with Vpx? b. Are there other Vpx- interactive proteins, and do they interact with Vpr?